Synthetic plastic broom bristles



Nov. 9, 1965 c. GoULD ETAL 3,216,038

SYNTHETIC PLASTIC BROOM BRISTLES Filed Nov. l, 1963 2 Sheets-Sheet l Ell-ga. @i

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AT TURNEY Nov. 9, 1965 c. GouLD ETAL 3,215,038

SYNTHETIC PLSTIC BROOM BRISTLES Filed Nov. l, 1963 2 Sheets-Sheet 2 BHARNA BDULD .AND MlLJAM EUULD rzkw' MMM...

ATTURNEY.'

United States Patent O 3,216,638 SYNTHETIC PLASTIC BROOM BRISTLES Charna Gould and William Gould, vboth of 280 Badger Ave., Millburn, NJ. Filed Nov. 1, 1963, Ser. No. 321,718 8 Claims. (Cl. 15-159) The present application is a continuation-inpart of application Serial No. 253,561, filed January 24, 1963, now abandoned.

The present invention relates to :synthetic plastic broom bristles, especially for use in large rotary street sweeping brooms of the type employed by municipalities, highway departments, etc. Such brooms comprise a core having a spiral groove extending for its length in which the radially extending bristles are secured by bending a length of bristle material at its center into V or U form and engaging the bight of the bent bristle material within the groove Where it is anchored under a retaining cable. When the bristles become worn they are removed and renewed, and the usual practice is for the broom user to perform the bristle renewing job with its own winding machines and personnel.

The synthetic plastic bristles require linear orientation of their ibres in order to impart to the material the advantageous characteristics of long wear, required degree of stiffness, inherent `springiness and bend recovery, improved sweeping, and increased resistance to the elements and extreme conditions of heat or cold. Conversely, oriented synthetic plastic bristles present diflicult problems in the broom assembly, their increased resistance to bending and their slippery surface making it difficult to manually manipulate and form the material into the usual V or U shape to enable it to be anchored in the core groove under the retaining cable. The stressed bight of the bent bristle tends to Slip and twist in the core groove and requires the holding cable to be braked under tremendous pressure in order to pull it into the core groove and retain it. The constant iight of the stressed material under the cable often results in the cable loosening prematurely causing the broom to fall apart. It is also diflicult to manually bend the bristles exactly in their center, resulting in an uneven broom face. Under these conditions the winding of a broom with synthetic plastic bristles is a slow, arduous one, and in the average city garage the groom Winder seldom winds enough brooms to develop the sensitive skill required to do a top notch job. The winding of a single broom usually requires the services of two men working three or four hours.

It is proposed according to the invention to provide a synthetic linearly oriented plastic bristle including a central core engaging area having relatively greater bendability and less bend recovery than the remainder of the bristle. To this end it is particularly proposed to stress relieve or relax a short section of the oriented fibrous bristle extending at each side of its center, this condition according to one aspect of the invention being conveniently attained in the case of thermoplastic linearly oriented material, such for example as nylon, polypropylene and the like, through the local application of heat to the center section at the controlled temperature required to stress relieve or relax the oriented brous structure, the low heat conductivity of such material being such that the 3,216,038 Patented Nov. 9, 1965 rate or delaminate to thus render the central area less resistant to bending. Such compressive deformation may be produced by suitable press-ure tools, with the bristle either in a cold or a suitably heated state, and such tools may preferably be such as to corrugate the opposed surfaces of the filament to provide in effect a hinge-like central area.

While the invention may be embodied in individual separated bristles, it is further proposed to provide a succession of bristles secured together along or adjacent their central relaxed areas in the form of a mat. Such mat may be provided in suitable short lengths, in continuous lengths, in coils, and in one or more layers depending upon particular requirements. As a further modilication it is proposed to pre-form the individual separated bristles, or the succession of bristles secured together in mat form, into substantially V shape to facilitate the assembly of the bristles in the broom, the pre-formed shape relieving pressure required to pull the bristles into the core groove, and also resulting in a more uniform broom face.

Other advantages of the pre-assembled mats are that they are easier to handle, particularly to the novice broom winder, 4eliminating the need of guesswork in determining how much bristle material to place under the core cable for a given area and allowing for more uniform dispersal of the bristles under the cable. Plastic bristles are inherently tough, springy, and slippery and the usual practice is to feed them under the core cable in hand-sized bundles, picked by the feel of the broom winder, with the result that the broom can be heavily filled, lightly filled, or spotty filled, depending upon the skill of the broom winder, there being no controlled consistency. With the pre-assembled mats of the invention the broom can be engineered for light or heavy use by inserting one, two or more layers of mats under the cable while winding, instead of depending upon guesswork as with the hand-filled method, the exact weight of the required broom can be predetermined with uniform till and bristle spacing, and a novice can fill a broom core as easily as the experienced broom Winder.

Other objects and advantages will become apparent from a consideration of the following detailed description taken in connection with the accompanying drawings wherein a satisfactory embodyment of the invention is shown. However, it will be understood that the invention is not limited to the details disclosed but includes all such variations and modifications as fall within the spirit of the invention and the scope of the appended claims.

In the drawings:

FIG. 1 is a perspective View showing a street sweeping broom partially filled with bristles;

FIG. 2 is anenlarged sectional view, partially in section and partially in elevation, showing the manner in which a bristle unit according to the invention is engaged and secured in the spiral core groove of a rotary broom;

FIG. 3 is a similar view showing the manner in which a bristle unit forming one of a series of units secured together in mat form according to the invention is en.

gaged and retained in the spiral core groove of a rotary broom;-

FIG. 4 is a perspective view of a bristle unit according to the invention;

FIG. 5 is a perspective view of a mat comprising a series of connected bristle units according to the invention;

FIG. 5a is a perspective view of a modiiied mat according to the invention;

FIG. 6 is a perspective view showing a bristle unit preformed into V shape according to the invention;

y FIG. 7 is a perspective view showing a mat of connected bristle units pre-formed into V shaped according to the invention;

FIG. 8 is a perspective view showing a mat of connected bristles having a pre-formed center groove formed therein according to the invention;

FIG. 9 is a greatly enlarged view partially in side elevation and partially in longitudinal section and With parts broken away of a bristle unit according to the invention;

FIG. 10 is a diagrammatic perspective view showing the manner in which a bristle mat as seen in FIG. 7 may be produced;

FIG. 11 is a greatly enlarged perspective View with parts broken away of a bristle unit of oval cross-section with a pressure deformed central area;

FIG. 12 is a plan view of the bristle unit illustrated in FIG. 1l;

FIG. 13 is a view partially in side elevati-on and partially in longitudinal section taken along the line 13--13 of FIG. 12;

FIG. 14 is a perspective view of a mat comprising a series of connected bristle units as illustrated in FIGS. ll-l3;

FIG. 15 is a perspective view showing the bristle unit of FIGS. ll-l3 pre-formed in V shape; and

FIG. 16 is a perspective View showing the mat of FIG. 14 pre-formed into V shape.

Referring to FIG. 1 of the drawings, the partially filled rotary sweeper broom illustrated by way of example comprises a core 10 secured upon an axle 11 and provided along its length with a spiral groove 12 in which the bristle material 13 is retained by a cable 14. The winding and filling of a broom of this type is carried out in a machine which rotates the core and exerts braking tension upon the cable, the latter being fastened at its lead end at the beginning of the spiral groove and fastened at its terminal at the end of the groove upon completion of the winding land filling operation. As the cable is fed into the grove the bristle material is folded about the cable so that the bight of each bristle unit is pressed and retained in the groove with its straight leg portions projecting radially from the groove.

The bristle unit 15 according to the invention is in the form of a length of synthetic thermoplastic material, for example nylon, polypropylene or the like, and is preferably an extruded filament of circular cross section, the linear orientation of the libres of the thermoplastic material being brought about by procedures involving the heating, stretching, and quenching of the extruded filament. A preferred form of filament from which lengths of the bristle units may be cut is disclosed in our pending application for Synthetic Filaments and Method of Making the Same, Serial No. 277,630 filed May 2, 1963 as a continuation-impart of applications Serial No. 131,- 137 filed August 14, 1961, now abandoned, and Serial No. 162,469 filed December 27, 1961, now abandoned, and which, as sh-own herein in FIG. 9, comprises a core 16 in which the fibres of the thermoplastic material are linearly oriented to a relatively high degree and a homogeneous casing 17 fused to the core. As disclosed in said application melted thermoplastic material is extruded as a filament which is then subjected to a fibre orienting step which produces linear orientation of the libres throughout the lila-ment to a degree in excess of that normally practiced. Thereupon the lilament is subjected to heat to remelt the surface area to a suliicient depth to produce .a homogeneous casing fused to a highly oriented fibrous core. The resultant filament has the high degree of stiff= ness, springiness, and bend recovery suitable for boom bristle use and at the same time presents a smooth tough surface highly resistant to splintering and splitting under the rugged conditions encountered in street sweeping.

In accordance with the invention the bristle unit is provided at its center portion with a stress relieved or relaxed area 18 which is substantially less resistant to bending and substantially more resistant to bend recovery than the remainder of the bristle unit. The relaxed area may according to one aspect of the invention be conveniently produced by subjecting the bristle material at its center portion to localized heat suliicient to stress relieve or relax the oriented fibres, the thermoplastic material having a low degree of heat conductivity so that the extent of the relaxed area may be accurately predetermined and controlled. The bristle unit may be easily bent upon itself at the relaxed area and the bend will be under a very low degree of stress with consequent less tendency to straighten. As seen in FIG. 2 the bristle unit is bent at its relaxed area 18 about the cable 14 and is pressed into the spiral core groove 12 and retained by the tensioned cable. The extent of the relaxed area is less than half the circumference of the cable so that the stiff springy leg portions of the bristle unit are also clamped in the groove contiguous to the relaxed area and are therefore firmly supported for flexing during the sweeping operation.

In FIG. 5 there is illustrated a modiiication in which a succession of the bristle units 15 are secured together along their central portions 18 to fonm a mat 15a which may be furnished in short lengths, continuous lengths, and in coils, depending upon the manner it is desired to assemble the bristles in the broom. Also, the mat may be assembled in the broom either as a single layer or if desired two or more layers may be superimposed. The bristle uni-ts may be secured at their center portions by any suitable means as for instance cementing or heating sealing, sewing, welding, or the like. Preferably the bristle units are secured together as illustrated by means of a thermoplastic strip 19 which may be applied as a hot extrudate of suitable plasticity in its hot state to heat seal or fuse to the center portions of the bristle units. The strip 19 may be subjected to the action of suitable rollers to form and press it into intimate relation with the bristle units.

FIG. 3 illustrates the manner in which the mat is assembled in the broom, the bristle units 15 being bent at their central stress relieved or relaxed portions 18 about the cable 14 and being pressed and retained in the spiral core groove 12 by the cable, the strip 19 at the same time being transversely bent in interposed relation 'between the cable and the bight of the bristle units. As clearly seen in FIG. 3 the width of the strip 19 is greater than the length of the relaxed portion 18 of the bristle unit and at least equal to half the circumference of the cable 14,. so that the marginal portions are interposed between the cable and the stiff springy leg portions contiguous to the relaxed area and the leg portions are thus firmly supported for flexing during the sweeping operation.

In FIG. 5a there is illustrated a modiiied mat 15b in which the bristle units are secured together by suitabley means adjacent to and at each side of their center por-- tions 18, such means preferably being in the form of a pair of thermoplastic strips 19-19 secured in similarmanner to the strip 19 in FIG. 5. When assembled inthe.

In FIG. 6 there is shown a modification in which the 4bristle unit is pre-bent into V shape at the central relaxed portion 18, and in FIG. 7 there is shown a modification in which the mat 15a of FIG. 5 is similarly pre-bent into V shape. Obviously, as Va further modification, the mat 15b of FIG. 5a may be similarly pre-bent into V form, This facilitates the assembly in the broom, eliminating the necessity for either manual or mechanical bending into relation with the cable. The pre-bending may be accomplished by bending in a heated state and quenching to set the bend.

In FIG. 8 there is shown a further modification in which the mat 15C is pre-grooved as at 20 along the central relaxed portions 1S of the bristle units 15 which are secured together in mat form by a pair of strips 19-19 in similar arrangement to the strips 19-19 of FIG. 5a. The grooving may be accomplished by forming the groove with the thermoplastic material in a heated state and then quenching to set the groove.

The bristle units may be of any suitable cross-sectional shape, the preferred shape 'being oval or elongate with the bending axis of the bight of the bent unit parallel to the major dimension.

In FIG. l there is diagrammatically shown the manner in which the bristle units may be produced, and in particular the manner in which the V shaped mat as seen in FIG. 7 may be produced. The side-by-side bristle units are guided along an inclined chute 21 between pairs of conveyor belts 22 which support the succession of bristle units adjacent their ends and move their central portions between heating elements 23 and 24 which supply the necessary controlled and localized heat to produce the stress relieved or relaxed center areas 18. As the bristle units leave the heating elements their center areas pass Ibeneath the nozzle 25 of an extruder 26 which deposits the thermoplastic strip 19 in the form of a hot extrudate which then moves between forming and pressing rollers 27 and 28. The mat is next guided upon a suitable platform 29 between Iforming rollers 30 and 31 which bend the mat of bristle units into V shape, the bend being set by subjecting it to suitable heating and quenching means. Obviously, particular steps in the described procedure can be eliminated to produce either the separate bristle units as seen in FIG. 4 or the fiat mat of bristle units as seen in FIG. 5. In producing the mats 15b and 15C of FIGS. and S the extruder would be provided with a pair of suitably spaced nozzles to produce a pa-ir of strips 19-19, and in pregrooving the mat 15C of FIG. 8 the groove 20 would be produced by substituting suitable grooving means for the bending means illustrated in FIG. 10.

In FIGS. 11-13 there is illustrated a modified bristle unit 15 in which the central portion 18 yis relaxed or stress-relieved by subjecting it to a compressive `deformation `or crushing action, for example by means of suitably shaped pressure dies or rolls to compress such central area and impress transverse corrugations 32 in its opposed surfaces. Preferably the bristle un-it is of oval cross-section and the corrugations extend parallel to its major dimension. The compressive action is such that the plastic material is permanently compressed in one direction and expanded in the other direction, and the linearly oriented fibres of the fibrous core 16 are deformed from their normal position with a consequent separation or breaking up of their continuity, the homogeneous casing 17 being such that the surface is not ruptured or fibrillated. The central section is thus relaxed or stress-relieved, and consequently has relatively greater bendability and less bend recovery than the remainder of the bristle extending at each side `of the central area. The transverse corrugations impart to the central area a hinge-like structure whereby the bending direction is oriented about an axis parallel to the corrugations. The compression of the central area may be carried out either in a cold state or suitably heated.

The crushed center portion 18 -of the bristle is such that the slippery hard outer surface is made easier to 6 handle and the packed fibres are loosened. In this condition the bristle yields best to the cable pressure, packs better in the groove, conforms to contiguous ybristles and is less subject to slippage under the cable while the broom is working.

In FIG. 14 a plurality of bristle units as shown in FIGS. ll-Jl3 are secured together to form a mat 15d preferably by means of a pair of thermoplastic strips 19-19 disposed at each side of the central portions 18. In FIG. l5 a bristle unit is shown pre-bent into V shape, and in FIG. 16 a mat 15d as seen in FIG. 14 is shown pre-bent into V shape. The pre-bending may be accomplished by bending in a suitably heated state and quenching to set the bend.

What is claimed is:

1. As a new article of manufacture, a broom bristle unit adapted to be bent upon itself into substantially U-form for assembly in a broom core of the type having a groove to receive the bight of the bent bristle with a retaining cable engaged Within said bight, said bristle unit comprising a filament of synthetic thermoplastic material in which the fibres are linearly oriented to impart stiff springiness to said filament and including a central portion and stiff springy bristle forming portions extending therefrom, said central portion having its linearly oriented fibres stress releived to impart relatively greater bendability and relatively less bend recovery to said central portion than said bristle forming portions, whereby said bristle unit is predisposed to bending to form a bight Within said central portion when said bristle unit is bent upon itself preparatory to insertion in said groove of said broom core.

2. The invention as defined in claim 1, wherein said filament comprises a fibrous linearly oriented core and a homogeneous casing fused to said core.

3. The invention as defined in claim 1, wherein said central portion is provided with impressed formations, and wherein the fibres of said central portion have a lesser degree of continuity and adherence than the fibres of said bristle forming portions.

4. The invention as defined in claim 1, wherein said central portion is provided with impressed transverse corrugations at two opposite sides, and wherein the fibres of said central portion have a lesser degree of continuity and adherence than the fibres of said bristle forming portions.

5. The invention as defined in claim 1, wherein said filament comprises a fibrous linearly oriented core and a homogeneous casing fused to said core, wherein said central portion is provided with impressed formations, and wherein the fibres of said core of said central portion have a lesser degree of continuity and adherence than the fibres of said bristle Vforming portions.

6. The invention as defined in claim 1, wherein said filament comprises a fibrous linearly oriented core and a homogeneous casing fused to said core, wherein said central portion is provided with impressed transverse corrugations at opposite sides, and wherein the fibres of said central portion have a lesser degree of continuity `and adherence than the fibres of said bristle forming portions.

7. The invention as defined in claim 1, wherein said filament is of oval cross-section, wherein said central portion is provided with impressed transverse corrugations at opposite sides substantially parallel to the major axis of said oval cross-section, and wherein the fibres of said central portion have a lesser degree of continuity and adherence than the fibres of said bristle forming portions.

8. The invention as defined in claim 1, wherein said filament is of oval cross-section and comprises a fibrous linearly oriented core and a homogeneous casing fused to said core, wherein said central portion is provided with impressed transverse corrugations at opposite sides substantially parallel to the major axis of said oval crosssection, and wherein the fibres of said central portion have a lesser degree of continuity and adherence than the fibres of said bristle forming portions.

References Cited by the Examiner UNITED STATES PATENTS 8 Luboshez 264-339 X Jones 161-175 X Press 264-339 X Lechene 15-182 X Peterson 15-189 X Moss 15-229.0 Munt 15-159.1

CHARLES A. WILLMUTH, Primary Examiner. 

1. AS A NEW ARTICLE OF MANUFACTURE, A BROOM BRISTLE UNIT ADAPTED TO BE BENT UPON ITSELF INTO SUBSTANTIALLY U-FORM FOR ASSEMBLY IN A BROOM CORE OF THE TYPE HAVING A GROOVE TO RECEIVE THE BIGHT OF THE BENT BRISTLE WITH A RETAINING CABLE ENGAGED WITHIN SAID BIGHT, SAID BRISTLE UNIT COMPRISING A FILAMENT OF SYNTHETIC THERMOSPLASTIC MATERIAL IN WHICH THE FIBRES ARE LINEARLY ORIENTED TO IMPART STIFF SPRINGINESS TO SAID FILAMENT, AND INCLUDING A CENTRAL PORTION AND STIFF SPRINGY BRISTLE FORMING PORTIONS EXTENDING THEREFROM, SAID CENTRAL PORTION HAVING ITS LINEARLY ORIENTED FIBRES STRESS RELIEVED TO IMPART RELATIVELY GREATER BENDABILITY AND RELATIVELY LESS BEND RECOVERY TO SAID CENTRAL PORTION THAN SAID BRISTLE FORMING PORTIONS, WHEREBY SAID BRISTLE UNIT IS PREDISPOSED TO BENDING TO FORM A BIGHT WITHIN SAID CENTRAL PORTION WHEN SAID BRISTLE UNIT IS BENT UPON ITSELF PREPARATORY TO INSERTION IN SAID GROOVE OF SAID BROOM CORE. 